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Performance of MHD Insulating Materials in a Potassium Environment

Description: The objectives of this study are to evaluate the compatibility of the MHD insulating materials boron nitride and silicon nitride in a potassium environment at temperatures of 1000 and 1400{degrees}F (538 and 760{degrees}C, respectively) and to measure the electrical conductivities of the specimens before and after exposure to potassium. Based on the test results, an assessment is to be made of the suitability of these materials for application as insulator materials in an MHD channel.
Date: December 1, 1991
Creator: Natesan, K.; Park, J. H.; Rink, D. L. & Thomas, C. A.
Partner: UNT Libraries Government Documents Department

Magnitude and Frequency of Floods in Small Drainage Basins in Idaho

Description: Abstract: A method which relates basin characteristics with peak flow characteristics is presented for determining magnitude and frequency of floods on streams with drainage areas between 0.5 and 200 square miles. Regression equations for each of eight regions are presented for determination of the 10-year flood. Peak flows for the 25- and 50-year floods can then be estimated from ratios developed for each region. Regression equations are not developed because of poor definitions for several areas that total about 20,000 square miles. The equations were based on multiple-regression techniques using annual peaks and basin characteristics for 303 gaged sites.
Date: April 1973
Creator: Thomas, C.A.; Harenberg, W. A. & Anderson, J. M.
Partner: UNT Libraries Government Documents Department

Characterizing high energy spectra of NIF ignition hohlraums using a differentially filtered high energy multi-pinhole X-ray imager

Description: Understanding hot electron distributions generated inside hohlraums is important to the ignition campaign for controlling implosion symmetry and sources of preheat. While direct imaging of hot electrons is difficult, their spatial distribution and spectrum can be deduced by detecting high energy x-rays generated as they interact with the target materials. We used an array of 18 pinholes, with four independent filter combinations, to image entire hohlraums with a magnification of 0.87x during the hohlraum energetics campaign on NIF. Comparing our results with hohlraum simulations indicates that the characteristic 30 keV hot electrons are mainly generated from backscattered laser plasma interactions rather than from hohlraum hydrodynamics.
Date: May 11, 2010
Creator: Park, H; Dewald, E D; Glenzer, S; Kalantar, D H; Kilkenny, J D; MacGowan, B J et al.
Partner: UNT Libraries Government Documents Department

MULTI-KEV X-RAY YIELDS FROM HIGH-Z GAS TARGETS FIELDED AT OMEGA

Description: The authors report on modeling of x-ray yield from gas-filled targets shot at the OMEGA laser facility. The OMEGA targets were 1.8 mm long, 1.95 mm in diameter Be cans filled with either a 50:50 Ar:Xe mixture, pure Ar, pure Kr or pure Xe at {approx} 1 atm. The OMEGA experiments heated the gas with 20 kJ of 3{omega} ({approx} 350 nm) laser energy delivered in a 1 ns square pulse. the emitted x-ray flux was monitored with the x-ray diode based DANTE instruments in the sub-keV range. Two-dimensional x-ray images (for energies 3-5 keV) of the targets were recorded with gated x-ray detectors. The x-ray spectra were recorded with the HENWAY crystal spectrometer at OMEGA. Predictions are 2D r-z cylindrical with DCA NLTE atomic physics. Models generally: (1) underpredict the Xe L-shell yields; (2) overpredict the Ar K-shell yields; (3) correctly predict the Xe thermal yields; and (4) greatly underpredict the Ar thermal yields. However, there are spreads within the data, e.g. the DMX Ar K-shell yields are correctly predicted. The predicted thermal yields show strong angular dependence.
Date: November 4, 2010
Creator: Kane, J O; Fournier, K B; May, M J; Colvin, J D; Thomas, C A; Marrs, R E et al.
Partner: UNT Libraries Government Documents Department

High aspect ratio hard x-ray (> 100 keV) imager to measure hot electron preheat for indirectly driven capsule implosions on the National Ignition Facility

Description: We have fielded a multi-pinhole, hard x-ray (> 100 keV) imager to measure the spatially-resolved bremsstrahlung emission from energetic electrons slowing in a plastic ablator shell during indirectly driven implosions at the National Ignition Facility. These electrons are generated in laser plasma interactions, and are a source of preheat to the deuterium-tritium fuel that could limit the compressibility required for ignition and burn. Our hard x-ray imaging measurements allow to set an upper limit to the DT fuel preheat, which we find is acceptable in current capsule implosions on the NIF.
Date: May 1, 2012
Creator: Doppner, T; Dewald, E; Divol, L; Burns, S; Izumi, N; Kline, J et al.
Partner: UNT Libraries Government Documents Department

Performance of MHD insulating materials in a potassium environment

Description: The objectives of this study are to evaluate the compatibility of the MHD insulating materials boron nitride and silicon nitride in a potassium environment at temperatures of 1000 and 1400{degrees}F (538 and 760{degrees}C, respectively) and to measure the electrical conductivities of the specimens before and after exposure to potassium. Based on the test results, an assessment is to be made of the suitability of these materials for application as insulator materials in an MHD channel.
Date: December 1, 1991
Creator: Natesan, K.; Park, J.H.; Rink, D.L. (Argonne National Lab., IL (United States)) & Thomas, C.A. (USDOE Pittsburgh Energy Technology Center, PA (United States))
Partner: UNT Libraries Government Documents Department

National Ignition Campaign Hohlraum Energetics

Description: The first series of experiments on the National Ignition Facility (NIF) [E. I. Moses, R. N. Boyd, B. A. Remington, C. J. Keane, and R. Al-Ayat, 'The National Ignition Facility: ushering in a new age for high energy density science,' Phys. Plasmas 16, 041006 (2009)] tested ignition hohlraum 'energetics,' a term described by four broad goals: (1) Measurement of laser absorption by the hohlraum; (2) Measurement of the x-ray radiation flux (T{sub RAD}{sup 4}) on the surrogate ignition capsule; (3) Quantitative understanding of the laser absorption and resultant x-ray flux; and (4) Determining whether initial hohlraum performance is consistent with requirements for ignition. This paper summarizes the status of NIF hohlraum energetics experiments. The hohlraum targets and experimental design are described, as well as the results of the initial experiments. The data demonstrate low backscattered energy (< 10%) for hohlraums filled with helium gas. A discussion of our current understanding of NIF hohlraum x-ray drive follows, including an overview of the computational tools, i.e., radiation-hydrodynamics codes, that have been used to design the hohlraums. The performance of the codes is compared to x-ray drive and capsule implosion data from the first NIF experiments. These results bode well for future NIF ignition hohlraum experiments.
Date: November 16, 2009
Creator: Meezan, N B; Atherton, L J; Callahan, D A; Dewald, E L; Dixit, S N; Dzenitis, E G et al.
Partner: UNT Libraries Government Documents Department

Hohlraum Designs for High Velocity Implosions on NIF

Description: In this paper, we compare experimental shock and capsule trajectories to design calculations using the radiation-hydrodynamics code HYDRA. The measured trajectories from surrogate ignition targets are consistent with reducing the x-ray flux on the capsule by about 85%. A new method of extracting the radiation temperature as seen by the capsule from x-ray intensity and image data shows that about half of the apparent 15% flux deficit in the data with respect to the simulations can be explained by HYDRA overestimating the x-ray flux on the capsule. The National Ignition Campaign (NIC) point-design target is designed to reach a peak fuel-layer velocity of 370 km/s by ablating 90% of its plastic (CH) ablator. The 192-beam National Ignition Facility laser drives a gold hohlraum to a radiation temperature (T{sub RAD}) of 300 eV with a 20 ns-long, 420 TW, 1.3 MJ laser pulse. The hohlraum x-rays couple to the CH ablator in order to apply the required pressure to the outside of the capsule. In this paper, we compare experimental measurements of the hohlraum T{sub RAD} and the implosion trajectory with design calculations using the code hydra. The measured radial positions of the leading shock wave and the unablated shell are consistent with simulations in which the x-ray flux on the capsule is artificially reduced by 85%. We describe a new method of inferring the T{sub RAD} seen by the capsule from time-dependent x-ray intensity data and static x-ray images. This analysis shows that hydra overestimates the x-ray flux incident on the capsule by {approx}8%.
Date: October 19, 2011
Creator: Meezan, N B; Hicks, D G; Callahan, D A; Olson, R E; Schneider, M S; Thomas, C A et al.
Partner: UNT Libraries Government Documents Department

Analysis of the National Ignition Facility Ignition Hohlraum Energetics Experiments

Description: A series of forty experiments on the National Ignition Facility (NIF) [E. I. Moses et al., Phys. Plasmas 16, 041006 (2009)] to study energy balance and implosion symmetry in reduced- and full-scale ignition hohlraums was shot at energies up to 1.3 MJ. This paper reports the findings of the analysis of the ensemble of experimental data obtained that has produced an improved model for simulating ignition hohlraums. Last year the first observation in a NIF hohlraum of energy transfer between cones of beams as a function of wavelength shift between those cones was reported [P. Michel, et al, Phys of Plasmas, 17, 056305, (2010)]. Detailed analysis of hohlraum wall emission as measured through the laser entrance hole (LEH) has allowed the amount of energy transferred versus wavelength shift to be quantified. The change in outer beam brightness is found to be quantitatively consistent with LASNEX [G. B. Zimmerman and W. L. Kruer, Comments Plasma Phys. Control. Fusion 2, 51 (1975)] simulations using the predicted energy transfer when possible saturation of the plasma wave mediating the transfer is included. The effect of the predicted energy transfer on implosion symmetry is also found to be in good agreement with gated x-ray framing camera images. Hohlraum energy balance, as measured by x-ray power escaping the LEH, is quantitatively consistent with revised estimates of backscatter and incident laser energy combined with a more rigorous non-local-thermodynamic-equilibrium atomic physics model with greater emissivity than the simpler average-atom model used in the original design of NIF targets.
Date: November 22, 2010
Creator: Town, R J; Rosen, M D; Michel, P A; Divol, L; Moody, J D; Kyrala, G A et al.
Partner: UNT Libraries Government Documents Department

Shock timing on the National Ignition Facility: First Experiments

Description: An experimental campaign to tune the initial shock compression sequence of capsule implosions on the National Ignition Facility (NIF) was initiated in late 2010. The experiments use a NIF ignition-scale hohlraum and capsule that employs a reentrant cone to provide optical access to the shocks as they propagate in the liquid deuterium-filled capsule interior. The strength and timing of the shock sequence is diagnosed with velocity interferometry that provides target performance data used to set the pulse shape for ignition capsule implosions that follow. From the start, these measurements yielded significant new information on target performance, leading to improvements in the target design. We describe the results and interpretation of the initial tuning experiments.
Date: October 24, 2011
Creator: Celliers, P M; Robey, H F; Boehly, T R; Alger, E; Azevedo, S; Berzins, L V et al.
Partner: UNT Libraries Government Documents Department